Shooting corner pins can be a challenge for many bowlers. More often than not, a bowler struggles with one side while the opposite side poses less of a challenge. Why is that? In many cases, it comes down to body alignment, which is a key point for improving your spare shooting.
Assuming that you already throw the ball straight (or relatively straight) at most of your spares, your physical alignment is very important. Many bowlers are often misaligned for their spare shots, either over-rotating or under-rotating their bodies in the stance, creating problems before they even start the approach.
Square your shoulders, hips, knees, and possibly your feet toward the pin you are trying to hit, not toward your target. Your target (likely an arrow) will probably fall slightly outside the visual path once your body is properly aligned to the corner pin.